1. Field of the Invention
This application relates to a process for purification of a solution. More particularly, this application relates to a process for removing heavy metal contaminants from a solution using an activated alumina adsorbent and optionally recovering the heavy metals.
2. Description of the Related Art
Historically, very little attention was paid to the disposal of industrial waste, due in part to lack of governmental regulation, and, more importantly, probably due to an overall lack of knowledge or appreciation by industry of the long term effects of industrial waste on people and the environment. Now, however, due both to government regulations and corporate responsibility, much attention has been addressed to proper handling and disposal of waste materials classified as hazardous or toxic.
Such materials include organics, heavy metals, cyanides, etc. Treatments for such materials include physical, chemical, biological, thermal, etc., depending upon the type of pollutant. Treatment of solutions containing heavy metals usually fall into the categories of physical and chemical. Most popular are the chemical treatments which treat the heavy metals to form compounds which will precipitate such as, for example, treatment with alkalies such as caustic soda or lime to form hydroxide precipitates or treatment with sulfur-containing compounds to form sulfides or sulfates.
Such methods for treating heavy metal pollutants are discussed in "Electroplating Wastewater Pollution Control Technology", by George C. Cushnie, Jr. published by Noyes Publications, Park Ridge, N.J. in 1985, at pp 1-9, 30-37, and 48-54; in an article published in Chemical Engineering on Aug. 6, 1984 at pp 51-64 entitled "Hazardous Waste Management: The Alternatives", by Mackie et al.; and in an article published in Chemical Engineering in September, 1985 at pp 60-74 entitled "Wastewater Treatment", by Eckenfelder, Jr. et al.
While such treatments work well for their intended purpose, i.e., to remove heavy metals from a plating solution or the like, they, in turn, create new problems. Conversion of heavy metal compounds to precipitates by neutralization, for example, as described in the aforementioned articles, forms hazardous sludge which must, in turn, be disposed of in an environmentally acceptable manner.
Other treatments have also been discussed for the removal of heavy metals from solutions such as electroplating solutions. Such methods, which are mentioned in the aforesaid Mackie et al. article on page 57, and the Eckenfelder Jr. et al. article on page 71, include: ion exchange, using caustic soda instead of lime to increase resin selectivity; activated-carbon adsorption: and reverse osmosis and evaporation.